Pulse comparator



March 19, 1957 s. LUBKIN PULSE COMPARATOR 3 Sheets-Sheet 1 Filed July50, 1952 ERROR INDICATING LAMPS 44 SWITCH 6 I llov ELECTRONIC ,SWITCH 40SYNC. LINE STANDARD COMPUTER 2s PULSE 6ENERATOR34 SWITCHZ AMPLIFIER 3OINVENTOR .SAMUEL L. UBKIN- BY 1 31 ATTORNEY 4 COMPARATOR 32 Fl 6. l

PULSE COMPARATOR Samuel Lubkin, Brooklyn, N. Y., assignor, by mesneassignments, to Underwood Corporation, New York, N. Y., a corporation ofDelaware Application July 30, 1952, Serial No. 301,751

7 Claims. (Cl. 250-47) This invention relates to pulse monitoringsystems and more particularly to a comparator suitable for comparing anexamined pulse with a standard pulse of proper shape, magnitude, andposition.

in the operation of electronic devices utilizing pulse type signals,such as high speed digital computers, it is important that the shape,amplitude, and the relative position of the pulses in the system bemaintained substantially constant in order to prevent defectiveoperation.

One of the major causes of pulse deviation is alteration in theelectrical characteristics of circuit components due to aging. This isparticularly true in the case of vacuum tubes. Although the design ofmost electronic devices utilizing pulse type signals is such that minorpulse deviations do not affect circuit performance, any major variationin pulse shape, amplitude, or position will result in defectiveoperation.

To prevent improper operation due to advanced deterioration of thepulses, it is desirable that various points in the circuitry be examinedor monitored in order to detect the earlier stages of pulse deviation.

An essential of any pulse monitoring system is a provision for pulseexamining. This may be accomplished by manually observing the pulse at adesired point in the circuitry using a suitable probe and oscilloscope.However, this procedure is relatively slow and requires highly skilledpersonnel. Additionally, manual pulse examination during the operationof the electronic device may be inconvenient, and may afiect propercircuit functioning.

' An object of the present invention, therefore, is to provide improvedapparatus for automatically and conveniently comparing an examined pulsewith a standard pulse in order to detect deviations in shape, amplitude,and position.

Another object of the invention is to provide pulse ited States Patentexamination apparatus which recognizes the legitimate absence of apulse.

A further object of the invention is to accurately indicate a pulsedeviation at an examined point in an' electronic device notwithstandingthe presence of random noise.

A still further object of the present invention is to provide apparatusof relatively .low cost for automatically examining a pulse fordeviations of shape, magnitude, and position.

The invention will be described in connection with a pulse monitoringsystem of the type described and claimed in my co-pending applicationSerial No. 300,383, filed July 23, 1952, and assigned to the sameassignee, now Patent No. 2,756,409 of July 24, 1956. The above system,which is particularly adaptable to the requirements of an electronicdigital computer, automatically functions to locate the exact point atwhich potentially dangerous pulse deviations occur before circuitfailure results; the detection taking place during the normal operationof the computer. p

In accordance with my invention, the examined pulse "ice is matched witha standard pulse of a given shape generated by a standard pulsegenerator. When the instantaneous magnitude of the examined pulse fallsbelow the instantaneous magnitude of the standard pulse, the comparatorproduces an error indication pulse.

A feature of the invention is a lower threshold detection device whichprevents the production of an error indication when the signal at theexamined point is less than a given value corresponding to the randomnoise level.

Other objects, features and advantages will appear in the subsequentdetailed description which is accompanied by drawings wherein:

Figure 1 is a diagrammatic illustration of an electronic digitalcomputer system embodying the invention;

Figure 2 shows another embodiment of the invention;

Figure 3 illustrates a feature of the comparator shown in Figure 2;

Figure 4 is a graph showing typical pulse wave forms which may occurduring the operation of the systems illustrated in Figures 1 and 2.

Description of system Referring to the system shown in Figure 1, arotary selector switch assemblage comprising the ganged switches Z, 4and 6 is automatically operated by the motor or switch drive 8 which iscoupled to the normally closed relay contacts 10 by connection 11. v Thecontacts 10 are connected to the positive terminal of power supply 12.The selector switch assemblage may be of the solenoid operated orcommutator types.

The ganged switches are identical and operate in unison.

Switch 2 includes the rotating member 14 which makes sequential contactwith the posts 16. Each of the posts 16 of the switch 2 is connected bya coaxial cable 18 to a point to be examined in the circuitry of thecomputer 25. The coaxial cable 18 is coupled to the examined point bymeans of the resistor 20 which is mounted in close proximity to theexamined point. (For purposes of description, only three examined pointsare shown. In actual operation many more positions are provided for.)The coaxial cable 18 is terminated by the resistor 22 connected betweenthe cable and ground. The post 16 is coupled to the junction 28 betweenthe resistor 22 and the coaxial cable 18. The outer conductor of thecoaxial cable 18 is grounded.

The points to be examined are sequentially connected by means of theswitch 2 to the amplifier 30, which, in turn, is connected to one inputof the comparator 32.

A standard pulse generator 34 is coupled to a second input ofthe'comparator 32 through the switch 4. The generator 34 is connected tothe computer 25 by the synchronizing line 36. Pulse generators are wellknown in the art and are available commercially. A suitable pulsegenerator is the General Radio Type 869A described in the General RadioCatalog M, October 1951, pages and 156, published in Cambridge,Massachusetts;

The output of the comparator 32 is connected via output connection 41 tothe electronic switch 40 which, in turn, is connected to relay 38 byconnection 37. The

normally open contacts 42 of relay 38 join the power supply 12 directlyto the buzzer or alarm 43, and via the switch 6 to the errorindicating'lamps 44, the remaining terminals of the alarm and lampsbeing connected to ground. Each lamp 44 is associated witha particularexamined point of the computer 25because of the coordinated operation ofthe switches 2 and 6.

The detailed structure and operation of the amplifier 30,-comparator 32and electronic switch 40 will be described more fully below after anexplanation of the operation of the pulse monitoring system.

Operation of system a particular point, and that pulse P1 of anamplitude of sixteen volts isa pulse of excellent amplitude and shape.

Pulse P2 illustrates the change in shape whichmay occur as theconstantsof the circuit components change.

The pulse magnitude is still sixteen volts, but the pulse isfmorerounded and the rise and fall times (the periods between minimum andmaximum amplitude)- have increased. The computer circuits are designedso that the pulse shape deviation indicated by pulse P2 will not'resultinerror production; however, itis advantageous to-know of this conditionin order to'p'revent further deterioration.

Other changes in the constants of the circuitry may producea pulse shapesimilar to that indicated as 'pulse P3. The magnitude of pulse P3 isgreater than twelve volts and will result in proper circuit operation,but the shape deterioration has reached a dangerous state and it isdesirable to avoid any furtherdeviation in order to prevent the futureproduction of erroneous results.

Pulse P4, with an amplitude slightly less than twelve volts, although ofgood shape is of too low a-magnitude and slight further deteriorationwill result in improper operation of the computer.

7 ever, certain abrupt types of circuit defects may result in suddenchange from a good'pulse to one of this type. Such a pulse may also beencountered without detection of previous deterioration when defectivecomputer components are replaced by components which havecharacteristics which do not meet the requirements of the circuit.

.Pu'lse P6, with an amplitude of less than three volts, will be utilizedto expl-ain'the operation of the invention in the presence of randomnoise. p 7

The position P7 is used to illustrate the operation of the invention inthe case of. the legitimate absence of 'a pulse at the. examined point.

, Pulse-P8 is an otherwise acceptable pulse which is 'dis-" placed intime position since it occurs too early.

Pulse P9, which is also properly shaped and of suf-.

.ficient amplitude, is displaced in time'position'since it occurstoolate.

As will be explained inmore detail hereinafter, the" invention'functionsto detect the marginal but acceptable pulses P2, Pfi'and Pe-before their shapes or magnitudes deteriorate further andcausecomputer error. The in- 1 vention also operates to detect-pulses ofunacceptable .magnitude of the 385 type and displaced pulses of the PBand P9 types. Furthenthis detection occurs coincident .with the'normaloperation of the computer, and the-system indicates the exact locationof the undesirable circuit component variations. 'However, a pulsedeviation is notv indicated in the :presence of. random. noise orwhen apulse is legitimatelyabsent -Referring again to'the system shown inFigure l, the resistor 20 serves to provide a high impedanceconnectionto the examined point in order to minimize computer. circuitdisturbanceand is chosen to be of relatively high resistance. Resistor22is chosen to equal the characteristic impedance of the coaxial cable 18in order to termi-. nate the cable properly.

"This choice of components'results in a'high impedance connectionbetween the "computerand the rest ofthe pulse monitoring system such;that ftlfl6;2 iti61'lll8.ti011 is subthe computer where the dangerexists.

stantially independent of frequency. Thus, the detected signal is madeproportional to the original examined pulse in amplitude and similar toit in shape. If the examined pulses vary considerably in amplitude frompoint to point in the circuitry, the resistance of the resistors 20 maybe chosen so that all signals are reduced to susbtantially the samecomparison level.

Due to the ;attenuation introduced 'by the high impedance coupling tothe computer, it is necessary to amplify the signal before examinationJThis-is the function of amplifier 3i ,which is operated as a linearamplifier in order to produce an output signal proportional to the inputsignal. The examined pulse (which will be used hereafter in place of thesignal representing the examined pulse) is compared with an amplifiedstandard pulse of a selected wave shape and twice the amplitude of asatisfactory computer pulse R, the amplified standard pulse S beingproduced by the standard pulse' generator 34. Synchronizing line 36functions to synchronize the standard and examined pulses to assureaccurate time coincidence of signals. There is also provision for anumber of different types of standard pulses depending on the desiredshape of the pulses at the examined points in the computer circuitry.Normally, a given standard pulse is used to check a number of differentpoints since desired pulse shapes and amplitudes are the same in manycircuits of the computer.

causing the relay 38 to energize signifying a'dangerous pulse deviation(pulses P2 to P5, P8 and P9).

if the examined pulse is less than three volts then no outpu'tpulse willbe produced. This is the situation in the'case .of thelegitimate absenceof a pulse at the examined point (position 7). Similarly, random noisedoes not affect the operation of the system since the noise magnitude is"normally less than three volts (pulse 6). Of course, if a pulse isproperly positioned and is of accepta'ble shape and magnitude, then nooutput pulse is produced (pulse P1),

When the relay 33 is energized, contacts 10 open and contacts 42 close.The opening of contacts It) removes the'power from the switch drive 8stopping the switch member 14 at a position correspondingto the point ini At the same time, the closing of contacts 42 energizes the alarm 43and lights the appropriate error indicating-lamps 44. Of course, insteadof stopping the switch at a position corresponding to a defective pointin the computer an annuncia-tor may beoperated without interfering withringthemonitoring operation and after the existence of padeviation'hasbeen indicated. Thereafter, during the and the relay 38 isreset.

normal computer maintenance period, the fault is rectifiedContinuous,monitoring system In some computer systems it may bedesirable to continue the scanning of the examined points during theentire computation period in order to detect additional pulse deviationsif they occur. 1 l

Continuous'monitoring, after an initial ,pulse deviation has beenregistered, may be obtained by using another embodiment of the inventionwhich will be described by specifyingminor modifications of theembodiment shown in'Figure 1'.

The following changes are made: Connection 11 from the switch drive 8 iscoupled directly to the positive terminal of power supply 12, and therelay 38 is not required (the contacts 42 are disconnected from theswitch member 15); the alarm 43 is disconnected from switch member 15;the error indicating lamps 44 are replaced by indicating devices whichwill maintain a particular state after operation, for example,annunciators; the output connection 37 of the electronic switch 40(which will be described more fully below) is connected directly to theswitch member 15 of the switch 6; the remaining terminals of theannunciators are connected to a voltage source, say one hundred fiftyvolts.

When a pulse deviation occurs a signal is produced by the comparator 32which operates the electronic switch 40. When the electronic switch 40is energized, current flows through the connection 37 and through theannunciator associated with the examined point, to operate theannunciator. When the switch member 15 moves to the next position, thecurrent flow is interrupted resetting the electronic switch 40. Thesystem is now capable of indicating pulse deviations which may occur atother examined points. The 'annunciators are reset during the nextmaintenance period after the computer is repaired.

Thus the invention provides for automatic operation of a pulsemonitoring system and indicates the exact location of pulse deviations,and does this without interfering with the normal operation of thecomputer. In addition, there is no erroneous indication due to randomnoise or the legitimate absence of a pulse at the examined point.'Further, continuous monitoring in order to detect additional pulsedeviations is easily achieved.

Description of amplifier 30, comparator 32, and electronic switch 40Referring again to Figure 1, the amplifier 30 comprises a linearamplifier 46 and a cathode follower 48. The linear amplifier 46 includesthe vacuum tube or electronic discharge device 50 having an anode 52, acontrol element or grid 54 and a cathode 56. The grid 54 is coupleddirectly to switch member 14 of switch 2. The anode 52 is connected to'a suitable voltage source 60, say one hundred fifty volts, by theresistor 64. The cathode resistor 62 connects the cathode 56 to groundand functions to bias the vacuum tube 50 and to provide degeneration.Degeneration occurs as the tube ages and the cathode emission drops, thecorresponding drop in current decreases the tube operating bias toneutralize the change in gain to a substantial extent.

The linear amplifier 46 is coupled to the cathode follower 48 by meansof a tapped resistor 65 connected between the anode 52 of the vacuumtube 50 and the displacement voltage source 63 of minus one hundred andfifty volts. The cathode follower comprises the vacuum tube 67 having ananode 68, a control grid 69, and cathode 70. The anode 68 is connectedto the voltage source 60 by a resistor 71. The grid 69 is connected tothe tap 66 on the resistor 65. The cathode 70 is grounded by means ofthe resistor 72 which provides bias and degeneration for the vacuum tube67.

The vacuum tube 50 is adjusted to operate as a linear amplifier bysuitable choice of circuit constants. lhe circuit constants of vacuumtubes 50 and 67, the position of tap 66 and the magnitude of the voltagesource 63 are chosen so that the examined pulse P is amplified anddisplaced to appear as pulse A (see line A) at the cathode 70 of thetube 67 having a shape substantially similar to the examined pulse butof a negative polarity and of twice the amplitude of the examined pulse.

-The amplifier 30 is coupled to the comparator 32 by means of the firstinput line 33 which is connected to the junction point A of resistors 74and 75 in series. The other end of resistor 74 is connected to the anode76 of the diode rectifier 78.

The junction point B of the diode 78 and the resistor 74 is connected tothe standard pulse genera-tor 34 via the resistor 73 and the secondinput line 35. More particularly, line 35 is connected to switch member80 of the switch 4. The resistors 73 and 74 are preferably chosen to beof equal resistance for reasons which will appear below. The cathode 82of the diode 78 is connected to ground via the resistor 96 and iscoupled by means of the capacitor 84 to the vacuum tube or electrondischarge device 86.

Vacuum tube 86 comprises the anode 88, the control grid 92, and thecathode 94 which is grounded. The capacitor 84is coupled directly to thecontrol grid 92 which is connected to a suitable negative bias source100, say minus five volts, by means of the resistor 98. The anode 88 iscoupled to a positive voltage source 105, which may be one hundred fiftyvolts, by means of the primary winding 132 of the pulse transformer'130.

The pulse transformer comprises the primary winding 132 and thesecondary winding 134. One terminal of the secondary winding 134 isconnected to a negative voltage source 135, say minus ten volts. Theother terminal of the secondary winding 134 is connected to the anode136 of the diode 138. The cathode of the diode 138 is connected to anegative voltage source 142, say minus sixty volts, by resistor 144, andto a negative voltage source 143, say minus eight volts, by the diode102. The cathode 103 of the diode 102 and the cathode 140 of the diode138 are connected together.

The cathode 103 of the diode 102 is also connected to a first controlgrid 152 of an electron discharge device or vacuum tube 150. Vacuum tube150, which functions as a gating device, includes an anode 154, a screengrid 156, a second control grid 158 and a cathode 160. The secondcontrol grid 158 is connected to the pulse generator 34 via the secondinput line 35 and the switch 4. The screen grid 156 is connected to asuitable voltage source 162, say seventy-five volts. The cathode 160 isgrounded. The anode 154 is connected to a suitable voltage source 164,say one hundred fifty volts, by means of the primary winding 166 of thepulse transformer 168. The secondary winding 170 of the pulsetransformer 168 has one terminal connected to a negative voltage source172, say minus ten volts, and the other terminal connected to the firstcontrol grid 152 of the vacuum tube 150 by means of the diode 174. Theanode 176 of the diode 174 is connected to the secondary winding 170 andthe cathode 178 of the diode 174 is connected to the control grid 152.-Vacuum tube 150, diodes 174 and 138 and transformer 168, in combination,act as a pulse extender or standardizing device.

Referring again to junction or point A, the remaining end of resistor 75is connected to the cathode 104 of the diode rectifier 105. The anode106 of the diode 105 is coupled to the control grid 114 of the vacuumtube or electronic discharge device 110 by means of the capacitor- 108.The vacuum tube 110 includes the anode 111 and the cathode 116. 1

The resistor 118, preferably of a resistance equal to that of resistor75, joins the anode 106 of the diode 105 to a threshold voltage source119 of minus six volts. The resistor 120 connects the control grid 114to a suitable negative source 122, of say minus five volts. The cathode116 of the tube 110 is connected to ground. The anode 111 is coupled toa positive voltage source 125, say one hundred and fifty volts, by meansof the primary winding 182 of the pulse transformer 180.

The pulse transformer comprises the primary winding 182, and thesecondary winding 184. One terminal of the secondary winding 184 isconnected to a negative voltage source 186, say minus ten volts. Theother terminal is connected to a first control grid of the elec trondischarge device or vacuum tube 192 through the diode rectifier 202.

The vacuum tube 192, which functions as a gating device, includes theanode 194,.the screen grid 196, a

second control grid 198'and the cathode 200. The-first jcontrolgrid-190;is connected to the, cathode 204fof the diode 202. The resistor208 links the cathode 204 of the diode 202 to a negative voltage source210, say minus sixty volts. The cathode 204 is also connected to anegative voltage source 211, say minus eight volts, by the diode 124.The cathode 125 of the diode 124 and'the cathode 204 of-the diode 202are connected'together.

The anode 206 of the diode 202 is connected to the winding 184. Thesecond control grid'198 is connected to the pulse generator 34 via. theswitch member 80 of the switch 4. The screengrid. 196 of the tube 192'is connected to a suitable positive voltage source 212', say plusseventy-five volts. The cathode 200 is grounded. T heanode 194 isconnected to the positive voltage source 21.4, of about one hundredand'fifty volts, by means of the primarywinding 216 of the pulsetransformer 218. The secondary winding 2200f the transformer 2 18connects a negative voltage source 222, minus ten volts, to the controlgrid 190 by means ofthe diode rectifier 224. The diode rectifier 224comprises the anode 226 connected to the winding 220, and the cathode228 connected to the control grid 190. Tube 192, diodes 224 and 202 andtransformer 218, in combination, act as a pulse extender orstandardizing device. Vacuum tubes 150 and 192 are transformer coupledto the electronic discharge deviceor vacuum tube 230, which functions asan electronic gate, by means of the transformers 168 and 218,

respectively.

The gating tube 230 includes a first control'grid 232 and a secondcontrol grid 234. Control grid 232 is conncctedto the junction point Ebetween the anode 176 of the diode 174 and the secondary winding 17 0,,of the pulse transformer 168. Control grid 234 is connected to thejunction point F between the anode 226 of the diode 224 and thesecondary winding 2200f the transformer 218.

The vacuum tube 230 also includes an anode 236, a screen grid 238 and acathode 240. The anode 236 is connected toa suitable voltage source 242,say one hundred and fifty volts, by means of the secondary winding 244of the output transformer 246. The screen grid 233 is connected to avoltage source 250 of about seventyfive volts. The cathode 240 isgrounded.

The output, transformer 246 includes the secondary Winding 24$having-one terminal connected to a negative voltage source 252 of.approximately minus ten volts. The other terminal of the secondaryWinding 2 .8 is coupled to the electronic switch.40 by-means of, theoutput connection 41.

The diodes are preferably of the germanium crystal type, but each may beany unilateral conducting device. The purpose of the diodes 136, 174,'202 and 224 is to isolate the associated transformers from each other.

T heelectronic switch 40. is more accurately described as a triggercircuit of'the gaseous tube type. The eiectronie switch 40 comprises anelectronic discharge device or thyratron 260 having an anode 262, acontrol grid 7 the relay 38 to'energize to indicate a pulse deviation asexplained. above.

The thyratron260 will'remain conductive until reset. 7 c

The switch 40 and the relay 38 may be reset by momentarily opening thereset switch 226 This interrupts the flowof anode current,tie-energizing the relay 38 and causing the gasin thetube 260tode-ionize. The

thyratron- 2 60 will not conduct thereafter until another positive pulseappears atthe control grid 264 to fire the thyratron 260. 7

Detailed operation of the comparator 32 Referringto-Figures l and 4,assume that a pulse. deviationindication is not desired when theexamined pulse P (on line P) is ofproper magnitude, and is properlyshaped and positioned. Assume further that pulse R (on line R) having amagnitude of twelve volts, represents the limiting pulse'such that it isdesired to detect any poorer pulse.

The upper level comparison section of the comparator (comprising thediode 78, the vacuum tube 86, andthe transformer determines Whether theexamined pulse is of deteriorated shape, deteriorated magnitude, or isdisplaced position. If any of these conditions exist, a pulse E (online'E) will appear at point E, the control grid 232 of the gating tube230, as will be hereinafter explained.

The signal representing the examined pulse is ampli-. fied and appearsat point A as the negative pulse A (on line A) having twice theamplitude of the examined pulse. The voltage at point B is the averageof the voltage at point A and the voltage at point S since the resistors73 and 74 are preferably chosen to be equal. However, any resistanceratio may be used with corresponding changes in the circuitry. The pulseB (on line B) which appears at pointB, therefore, is equal to thedifference between pulses R and P because the amplified standard pulse S(on line S) is of the same shape and twice the amplitude of pulse R.

The pulse C (on line C) which appears at point C is the positive portionof the pulse B since the cathode 82 of the diode 78 is at groundpotential and will only conduct when the anode76 becomes-positive. Thepulse C is amplified and inverted by amplifier tube 86 and reinverted bythe transformer 130 to appear as pulse H (on lineH) at'junction point Hof the anode 138 and the transformer secondary 134. I

For purposes of description assume that the amplification of theamplifier and the turns ratio of the transformer 130 are chosen. toresult in a pulse H of positive polarity having ten times the magnitudeof pulse C. Assume further that the pulse H will have a maximumamplitude of ten volts due to the saturation of amplifier tube 86, Thediodes 138 and 174 are normally nonconducting between pulses since theiranodes are at a lower potenial than their cathodes because diode 102 isnormally conducting and resistor 144 is chosen to have a relatively highresistance. When a pulse H greater than two volts is present, diodes 138and 17-:- conduct and diode 102 is disconnected.

The vacuum tube is adjusted so-that it will conduct when both controlgrids 152 and 158 are driven positive. Since control-grid 158 isconnected to the pulse generator, an output pulse will-be produced whenthe amplified pulse S and pulse H exist simultaneously.

The pulse H is stretched or standardized in the following manner: whenan output pulse is initiated, it is inverted by'the transformer 16% andappears across the secondary, 1'70 and is fed back to the control grid152 by means of the diode 174. This maintains the positive signal on thecontrol grid 152 until the standard pulse on control grid 158terminates. When the amplified standard pulse terminates, the tube 150does not conduct. In other words, if the'pulse H terminates before theamplified standard pulse E terminates, the pulse output is mantaineduntil the end of the amplified standard pulse and appears as a positivepulse E (on line E) at point E. Between pulses, undesired feedback andtherefore unwanted oscillation is prevented since the diode 174 becomesnonconducting due to the diode 102 andthe source 143. V

.' -Referringagain'topoint A, the lower level-comparison section(comprising the diode 105, the amplifier tube 110 and the transformer180) operates to impress a pulse at point F (the control grid 234 of thegatingtube 230). whenever the examined pulse P exceeds a magnitude ofthree volts, as will be explained hereinafter.

The voltage at point D will equal the average of the voltages appearingat point A diminished by six volts. This is because resistors 75 and 118are preferably chosen to be equal. However, any resistance ratio may beused with corresponding changes in the circuitry. Point D will bemaintained at a base level of minus six volts between pulses since theanode 106 is more negative than the cathode 104. When a pulse A appearsat point A, the diode 105 will not conduct until the magnitude of thepulse becomes less than minus six volts. The averaging of the Voltagesoccurs whenever the diode I conducts and a pulse D (on line D) ofnegative polarity is produced at point D. Pulse D is amplified by theamplifier tube 110 and appears as pulse I (on line I) at point I havingpositive polarity due to the inversion caused by the amplifier.

For purposes of description assume that the amplification of theamplifier tube 110 and the turns ratio of the transformer 130 are chosento result in a pulse I having ten times the magnitude of pulse D, with amaximum amplitude of ten volts due to the saturation of tube 110. Thevacuum tube 192 and the associated components function in a similarmanner as the vacuum tube 150 circuitry, that is, it stretches andstandardizes the input pulses. When an amplified standard pulse S and apulse I initially exists simultaneously, an output signal will bemaintained until the termination of the amplified standard pulse S. Theoutput pulse F (on line F) appears at point P, that is, the control grid234 of the gating tube 230.

The gating tube 230 will conduct when positive signals appearsimultaneously on the control grids 232 and 234. This will be the casewhen an examined pulse is greater than three volts and is either poorlyshaped, or less than twelve volts, or is displaced. An output pulse G(on line G) from gating tube 230 will fire the thyratron tube 260 toindicate a pulse deviation.

Of course, the invention is not restricted to the types of amplifiers,pulse standardizers, rectifiers, or gating circuits shown, and similarcomponents may be substituted.

The operation of the comparator 32 will be explained in more detail inconnection with the series of examined pulses P1 P9 as described aboveand as shown in Figure 4. The wave forms directly beneath the respectiveP pulses indicate the pulse shapes at the respective points in thesystem which occur when the indicated P pulse is examined.

P1, a pulse of excellent shape and magnitude, is amplitied and invertedby the amplifier 30 and appears at point A as indicated by pulse A1.Pulse B1 indicates the pulse shape at point B. Since B1 is entirelynegative, no pulse will appear at point C and consequently the uppersection will not impress a pulse on the grid 232 of the gating tube 230,thus preventing a pulse deviation indication.

Pulse P2, a poorly shaped pulse, will appear as pulse A2 at point A.Pulse B2 indicates the averaging of the pulse A and the pulse S. Thepulse E2 will appear at point E because a portion of pulse B is positiveas indicated by pulse C2. Since pulse P2 is greater than three volts, apulse F2 will appear at point P simultaneously, resulting in a pulsedeviation indication produced by the output pulse G2 which fires thethyratron 260 to operate the electronic switch 40.

Pulse P3, a pulse of marginal shape and magnitude will similarly producea pulse E3 at the gating tube simultaneously with the pulse F3, sincethe examined pulse has a magnitude greater than three volts. Theconsequent output pulse G3 will indicate a pulse deviation.

Although the pulse deterioration will normally occur in a predictablemanner, it is possible that a sudden change of shape may take placeproducing a pulse of,

the P4 type. Pulse P4 is a poorly shaped pulse having an unacceptablemagnitude, that is, a magnitude greater than three volts and less thantwelve volts. When an examined pulse in the shape of pulse P4 occurs, apulse C4 will appear at point C since a portion of pulse B4 is positive.The pulse C4 will be amplified and stand ardized to appear as pulse E4at the control grid 232 of the output gating tube 230. A pulse will alsoappear at the control grid 234 since the amplitude of pulse P4 isgreater than three volts. The resulting pulse G4 will indicate a pulsedeviation.

Pulses of the type P5 may also occasionally occur having a magnitude alittle greater than the lower threshold level of three volts; forexample, four volts. In this case particularly, the pulse standardizingcircuits substantially help to provide a more accurate pulse detectionsystem. This is because the pulse produced at the point I is relativelynarrow since only a small portion of the pulse P5 is above thethree-volt level. The pulse I5 appears at the gating tube 230simultaneously with the pulse F5 which is generated due to the fact thatthe magnitude of pulse P5 is less than twelve volts. It should be notedthat if the pulses at points H and I were applied directly to the outputgating tube 230, they might not occur simultaneously and thus notproduce an output pulse to fire the thyratron tube 260. The pulsestretching produced by the pulse standardizing tube 192 results inpulses which last until the end of the corresponding pulse S and hencecoexist at the end of that period.

Pulse P6 illustrates the operation of the comparator in'the presence ofsignals having magnitudes of less than three volts, for example, randomnoise. No pulse is produced at point D and therefore a pulse will notappearat point P, thus preventing the occurrence of a pulse deviationindication.

The position P7 on the line P indicates the operation of the comparatorwhen a pulse is legitimately absent at an examined point in thecomputer. The comparator functions in exactly the same manner as in thecase of the pulse P6 and no signal will appear at the output of thecomparator.

Pulse P8 is a pulse of proper shape and amplitude but occurs too early;in other words, it is displaced in position. Since the standard pulsesare properly timed, when the comparison is made between the pulse A andthe pulse S, the two pulses will coexist for only a small period of timeresulting in relatively narrow pulses at points C, H and E. Since thepulse P8 has a magnitude greater than three volts, pulse F8 will appearat point F simultaneously with the pulse E8 to produce an errorindicating pulse G8.

Pulse P9 illustrates an examined pulse which occurs too late. In thiscase, the relatively narrow pulse H9 produced at point H is stretched toproduce the pulse E9 at the gating tube 230 simultaneously with thepulse F9 to. indicate a pulse deviation. Therefore, when the pulse istoo late, the pulse stretching produced by the pulse standardizing tube151) functions to reduce the margin of error of the comparator.

It should be noted that the standard pulses are considerably narrowerthan the examined pulses. This is to allow'the examined pulse to rise toa point near its maximum magnitude before it is compared, otherwise afalse error might be indicated during the transient periods between themaximum amplitude and the base voltage.

For purposes of description the pulses are shown in theoreticallycorrect form. In actual operation, how ever, the pulses are more roundedthan illustrated, but this does not rafiect the proper operation of theinvention. V 7

Similarly, the pulses are shown in a number of discrete stages ofpossible deterioration although in practicethe shapes normally wouldvary continuouslyfrom one stage to another. Also, difierent types ofcircuit deterioration will produce various kinds of pulses, and

only a portion of the pulse shapes shown will appear at a particularpoint. A

In summary, an output pulse will appear at the output of the comparator,and thus indicate .a danger point, only when the following examinedpulse conditions appear simultaneously:

1. The examined pulse has a instantaneous amplitude which is less thanthe instantaneous amplitude of the standard pulse R.

2. The examined pulse has a maximum amplitude greater than three volts.7

The existence of the first condition indicates a deviation in pulseshape or magnitude, or'a displacement in pulse position. The secondcondition insures that. false danger signals will not occur when pulsesare legitimately absent or when random noise is present at the examinedpoint.

Comparator 32 Another embodiment of the invention is diagrammaticallyillustrated in Figure 2. The same elements are designated by the samereference characters as in Figure 1, while equivalent elements bearprime designations (amplifier 3t), comparator 32', standard mask 34' andstandard sweep generator 340'). This embodiment of the inventionfunctions in exactly the same way as the system explained above, thefundamental difference being in the method of comparison. The standardmask 34' and the standard sweep generator 34a cooperate to provide astandard of comparison.

The comparator 32 and standard mask 34 comprise an oscilloscope 3%, astandard mask 34', a photoelectric cell 316, and a photocell amplifier320.

Oscilloscopes are instruments which are commercially well known, such asthe General Electric Oscilloscope, Type ST2A. The oscilloscope 300 has acathode ray tube 3&2 with a standard mask 34 which partially masksthescreen 304 of the cathode ray tube 392, as shown in Figure 3. Theunmasked portion corresponds to the limiting pulse R (see Figure 4, lineR) except that the area below a magnitude of three volts is masked bythe standard mask 34'.

The examined pulse is amplified by the amplifier 30 which includes thevacuum tube 330 having an anode 332, a screen grid 334, a control grid336 and a cathode 338. The anode 332 is connected to a suitable voltagesource 340, say one hundred fifty volts, by the primary winding 344 ofthe transformer 342. One terminal of the secondary winding 346 isgrounded and the other is connected to the inputline 33. The screen grid334 is connected to a suitable voltage source 345, say seventyfivevolts. The control grid 336 is coupled to the ex- A 7 suitable voltagesource 3 54, say fiftyvolts.

type generally used in oscilloscope design. Since more than one standardsweep frequency is required, a corresponding number of sweep generatorsis necessary. Therefore, the sweep generator 34a is actually composed ofa number of separate generators although shown as one for purposes ofdescription.

The amplification of amplifier 30' and the magnitude of the voltagesource 354 are chosen so that the examined pulse will appear properlydisplayed on the screen 304 of the oscilloscope 300. If any portion ofthe displayed pulse appears in the unmasked portion of the screen 304,indicating a pulse deviation as explained above, the light is picked upby the photoelectric cell 310 which is positioned in front of thescreen. The screen 304, the standard mask 34, and the cell 310 areenclosed in a lightproof structure (not shown). The photocell 310 isconnectcdto the amplifier 320.

When a pulse deviation occurs, the photocell 310 converts the lightappearing as a trace on the unmasked portion of the screen 304 into anelectric current which is amplified by the photocell amplifier 320. Thephotocell amplifier 32t) is substantially the same as amplifier 30'although it may be any amplifier circuit. The output line 322 of thecomparator is connected between the transformer (not shown) of theamplifier 32% and the control grid 264 of the electronic switch 40. Theamplified signal which appears on the output line 322 when a pulsedeviation occurs, operates the electronic switch 40, as explained above,to indicate a pulse deviation.

Conclusion Thus the invention provides an improved method ofautomatically monitoring the shape, amplitude and position of pulse typesignals, and can detect dangerous deviations during the normal operationof the monitored device before the deviations become serious enough toresult in error production.

In addition, no error indication will be produced in the presence ofrandom noise or when an examined pulse is legitimately absent.

In order to simplify the explanation of the invention, all potentialsources used throughout this system have been indicated by theirindividual magnitudes and polarities. Also, pulse shapes and magnitudeshave been indlcated 'as having particular values. It will be understood,of course, that these magnitudes and polarities are not critical and theinvention is not so limited; the particular values are given by way ofillustration only. Also, the power supplies and heaters which may beutilized for bringing the thermionic cathodes .to operating temperaturehave not been discussed since these elements are well known tothoseskilled in the art.

The horizontal plate terminal 356 is connected by 1 ,means of the secondinput line 35 to the switch 4' which selects different sweep frequenciesfrom the standard sweep generator 34a depending on the characteristicsof the examined pulse at a particularpoint in the computer :25circuitry. The remaining horizontal plate terminal 358 is grounded.

.Any generator capable of producing periodic waves is suitable'for useas the sweep generator. Sweep gen; erators are commercially availableand may be of the While only a representative embodiment of theinvention disclosed herein has been outlined in detail, there will beobvious to those skilled in the art, many modifications and variationsaccomplishing the foregoing objects and realizing many or all of theadvantages,'but which yet do not depart essentially from'the spirit ofthe in- .yention.

' What is claimed is:

1. A comparator for comparing an examined pulse with a standard pulse ofa given shape, magnitude and position, and with a lower level thresholdvoltage having a magnitude greater than the random noise voltagecomprising: an upper level comparison means having a firstinput'connection, a second input connection, and an output connection,said first input connectionbeing responsive to the examined pulse, saidsecond input connection being responsive to the standard pulse, anoutput signal appearing at said output connection when the instantaneousmagnitude of the examined pulse falls'below the instantaneous magnitudeof the standard pulse; a lower level comparison means having a firstinput connection, a second input connection and an output connection,said first input connection of the lower level comparison means beingresponsive to the examined pulse, said second input connection of thelower level comparison means being responsive to the threshold voltage;the presence of a signal on said output connection of the lower levelcomparison means indicating a signal having a magnitude greater than themagnitude of the threshold voltage, the simultaneous appearance ofsignals on said output connections indicating a deviation in shape ormagnitude or position of the examined pulse; and gating means havingfirst and second input connections and an output connection, said firstinput connection of the gating means being connected to said outputconnection of the upper level comparison means, said second inputconnection of the gating means being connected to said output connectionof the lower level comparison means; a signal indicating a pulsedeviation appearing at said output connection of said gating means whensignals are present simultaneously at said first and second inputconnections of said gating means. i

2. A comparator for comparing an examined pulse with a standard pulse ofa given shape, magnitude and position, and with a given lower levelthreshold voltage having a magnitude greater than the random noisevoltage level comprising: an upper level comparison means having a firstinput connection, a second input connection, and an output connection,said first input connection being responsive to the examined pulse, saidsecond input connection being responsive to the standard pulse, anoutput signal appearing at said output connection when the instantaneousmagnitude of the examined pulse falls below the instantaneous magnitudeof the standard pulse; a lower level comparison means having a firstinput connection, a second input connection and an output connection,said first input connection of the lower lever comparison means beingresponsive to the examined pulse, said second input connection of thesaid lower level comparison means being responsive to the thresholdvoltage; the presence of a signal on said output connection of the lowerlevel comparison means indicating a signal having a magnitude greaterthan the magnitude of the threshold voltage; first pulse standardizingmeans having an input connection connected to said output connection ofthe upper level comparison means and an output connection; second pulsestandardizing means having an input connection connected to said outputconnection of the lower" level comparison means and an outputconnection; the'simultaneous appearance of signals on said first andsecond standardizing means output connections indicating a deviation inshape or magnitude or position of the examined pulse examined point; nopulse deviation being indicated when random noise is present at saidfirst input connections, no pulse deviation being indicated when a pulseis absent at said first input connections.

3. A comparator for comparing an examined pulse with a standard pulse ofa given shape, magnitude and position, and with a given lower levelthreshold voltage having a magnitude greater than the random noisevoltage level comprising: an upper level comparison means having a firstinput connection, a second input connection, and an output connection,said first input connection being responsive to the examined pulse, saidsecond input connection being responsive to the standard pulse, anoutput signal appearing at said output connection when the instantaneousmagnitude of the examined pulse falls below the instataneous magnitudeof the standard pulse; a lower level comparison means having a firstinput connection, a second input connection and an output connection,said first input connection of the lower level comparison means beingresponsive to the examined pulse, said second input connection of thelower level comparison means being responsive to the threshold voltage;the presence of a signal on said output connection of the lower levelcomparison means indicating a signal having a magnitude greater than themagnitude of the threshold voltage; first pulse standardizing meanshaving an input connection connected to said output connection of theupper level comparison means and an output connection; second pulsestandardizing means having an input connection connected to said outputconnection of the lower level comparison means and an output connection;the simultaneous appearance of signals on said first and secondstandardizing means output connections indicating a deviation in shapeor magnitude or position of the examined pulse; no pulse deviation beingindicated when random noise is present at said first input connections,no pulse deviation being indicated When a pulse is absent at said firstinput connections; said first and second pulse standardizing meansreducing the margin of pulse deviation indication error; and gatingmeans having first and second input connections and an outputconnection, said first input connection of the gating means beingconnected to said output connection of the first standardizing means,said second input connection of the gating means being connected to saidoutput connection of the second standardizing means, a signal indicatinga pulse deviation appearing at said output connection of the gatingmeans when signals are present simultaneously at the said first andsecond input connections of said gating means.

4. A comparator for comparing an examined pulse with 'a standard pulseof a given shape, magnitude, and position comprising a first resistorhaving one end responsive to the examined pulse, a second resistorhaving one end responsive to the standard pulse, a unilateral conductorhaving one end of predetermined polarity connected to the other ends ofsaid resistors, a third resistor connecting the other end of saidunilateral conductor to a point of fixed reference potential, theappearance of a pulse on said other end of the unilateral conductorindicating a deviation in shape or magnitude or position of the examinedpulse; and pulse standardizing means having a first control element, asecond control element and a controlled element, said first controlelement being connected to said other end of the unilateral conductor,said second control element being responsive to the standard pulse, andfeedback means connecting said controlled element to said first controlelement; an output pulse initially appearing at said controlled elementwhen the pulse indicating a pulse deviation and the standard pulse existsimultaneously, the output pulse being maintained until the terminationof the standard pulse.

5. A comparator for comparing an examined pulse with a lower levelthreshold voltage having a magnitude proportional to the random noisevoltage level comprising a first resistor having one end responsive tothe examined pulse, a unilateral conductor having one end ofpredetermined polarity connected to the other end of said firstresistor, a second resistor having one end connected to the other end ofsaid unilateral conductor, the other end of said second resistor beingresponsive to the threshold voltage, the presence of random noise atsaid first resistor not resulting in a signal across said secondresistor, a standard pulse source, and pulse standardizing means havinga first control element, a second control element and a controlledelement, said first control element being connected to said other end ofthe unilateral conductor, said second control element being connected tosaid standard pulse source, feedback means connecting said controlledelement to said first control element; an output pulse initiallyappearing at said controlled element when the pulse indicating a pulsedeviation and the standard pulse exist simultaneously, the output pulsebeing maintained until the termination of the standard pulse.

6. A comparator for comparing an examined pulse with a standard pulse ofa given shape, magnitude, and position and with a standard voltagehaving a magnitude proportional to the signal level of random noisecomprising: a first impeder having one end responsive to the examinedpulse, a second impeder having one end responsive to the standard pulse,a first unilateral con- 'nitude or position of the examined pulse; pulsestandardizing means having one end connected to said other end of thefirst unilateral conductor; gating means having ,a first input, a secondinput and an output, the other end of said pulse standardizing meansbeing connected to said first input of the gating means; a fourthimpeder having one end responsive to the examined pulse, a secondunilateral conducting device having one end of predeterminedtp olarityconnected to the other end of said fourthimpeder; a fifth impeder havingone end connected to theother end of said second-unilateral conductingdevice, the other end of said fifth impeder being responsive to thestandard voltage, the presence of random noise at saidone end of saidfourth impeder not resulting in a signal at said other end of the secondunilateral conducting device; and pulse standardizing means having oneend connected to said other end of the second unilateral conductingdevice, the other end of said pulse standardizing means being connectedto said second input of the-gating means; a signal appearing at theoutput of said gating means when an examined pulse has deviated in shapeor magnitude or position as compared with the standard pulse, no signalappearing at said output when random noise is present in place of theexamined pulse, no signal appearing at said output when an examinedpulse is legitimately absent.

7. A comparator for comparing an examined pulse with a standard pulse ofa given shape, magnitude, and position and with a standard voltagehaving a magnitude proportional to the signal level of random noisecomprising: a first resistorhaving one end responsive to the examinedpulse, a second resistor having one end reductor; first pulsestandardizing means having one end connected to the other end of saidfirst amplifier means; gating means having a first input, a second inputand an output, the other end of said first pulse standardizing meansbeing connected to said first input of the gating means; a fourthresistor having one end responsive to the examined, pulse, a secondunilateral conducting device having one end of predetermined polarityconnected to the other end of said fourth resistor, a fifth resistorconnected to the other end of said second'unilateral conducting device,the other end of said fifth resistor being responsive to thestandardvoltage, the presence of random noise in place of an. examined pulse notresulting in a signal at said other end of the second unilateralconducting device; second amplifier means having one end connected tosaid other end of the second unilateral conducting devicc; and secondpulse standardizing means having one end connected to theother end ofsaid second amplifier means, the other end ofsaid second pulsestandardizing means being connected to said second input of the gatingmeans; asignaljappearing at the output of said gating means when anexamined pulse has deviated in shape or magnitude. or position ascompared with the standard pulse, no signal appearing at said outputwhen random noise is'present, no signal appearing at said output when anexamined signal is legitimately absent.

References Cited in the file of this patent UNITED STATES PATENTS2,208,349 Ulbricht July 16, 1940 2,236,015 Sonnentag Mar. 25, 19412,266,401 Reeves Dec. 16, 1941 2,504,976 Grieg Apr. 25, 1950 2,557,729Eckert June 19, 1951 2,577,475 Miller ..2 Dec. 4, 1951 2,603,746Burkhart et a1. July 15, 1952 2,632,104 Lakatos Mar. 17, 1953 2,633,570Greenwood Mar. 31, 1953 2,649,543 Trachtenberg Aug. 18, 1953 2,658,142St. John Nov. 3, 1953 2,675,538 Malthaner et al. Apr. 13, 1954 2,676,253Ayres Apr. 20, 1954 2,676,286 Buchner Apr. 20, 1954 2,677,758 Robinsonet al. May 4, 1954 2,685,039 Scarbrough et a1 July 27, 1954 2,693,907Tootill Nov. 9, 1954

